Many cryotherapeutic procedures include introducing a cryo-catheter into a patient (e.g., into the vasculature of a patient) and cooling a cryo-applicator of the cryo-catheter using refrigerant. In some cases, refrigerant introduced into the cryo-catheter is chilled and circulated through the cryo-applicator without expanding significantly. For example, the cryo-catheter can be thermally insulated proximal to the cryo-applicator such that chilled refrigerant circulated through the cryo-catheter does not readily absorb heat from nearby tissue until it reaches the cryo-applicator. In other cases, refrigerant, which can be chilled or not chilled, expands significantly within the cryo-catheter and drops in temperature and/or absorbs heat from nearby tissue due to the Joule-Thomson effect alone or in combination with increasing latent heat. For example, refrigerant can enter the cryo-catheter partially or entirely in liquid phase at high pressure, expand and/or vaporize by passing through an orifice within the cryo-applicator, and then exit the cryo-catheter in gas phase at low pressure. Cooling via refrigerant expansion can be particularly useful in relatively long and narrow cryo-catheters (e.g., most intravascular cryo-catheters). In such cryo-catheters, for example, refrigerant cooling potential in the form of high refrigerant pressure can usually be maintained more readily than refrigerant cooling potential in the form of low refrigerant temperature while refrigerant is en route to a distal cryo-applicator.
In conventional cryotherapeutic systems configured for cooling by refrigerant expansion, resulting expanded refrigerant is typically exhausted to the atmosphere or collected for disposal. For example, a conventional cryotherapeutic system can be configured to be connected to a hospital scavenging system that transports expanded refrigerant to a centralized location for disposal. Both releasing expanded refrigerant into the atmosphere and transporting expanded refrigerant to a centralized location deplete the supply of refrigerant available to the system. Accordingly, conventional cryotherapeutic systems are typically configured to be connected to refrigerant supply tanks that must frequently be replaced or recharged. Replacing or recharging refrigerant supply tanks, however, can be logistically challenging and costly. Furthermore, although larger refrigerant supply tanks often require replacement or recharging less frequently than smaller refrigerant supply tanks, larger refrigerant supply tanks are also typically more obtrusive and cumbersome to handle than smaller refrigerant supply tanks.
Conventional cryotherapeutic systems are usually only compatible with certain types of refrigerants. For example, many conventional cryotherapeutic systems are configured for use with nitrous oxide, which can be released into the atmosphere or collected for disposal with little or no concern for toxicity or environmental impact. While nitrous oxide is a useful refrigerant, other refrigerants can have more advantageous thermodynamic properties (e.g., greater latent heats of vaporization) than nitrous oxide. These other refrigerants, however, are potentially more harmful to the environment than nitrous oxide. Intentionally and non-incidentally releasing and/or disposing of such refrigerants is, in many cases, prohibited by regulations, inconsistent with accepted medical protocols, or both. Thus, many potentially useful types of refrigerants are not available for use in conventional cryotherapeutic systems configured to release expanded refrigerant into the atmosphere or to collect expanded refrigerant for disposal. This can limit the performance of such systems.
For the reasons stated above and for other reasons, whether or not expressly disclosed herein, there is a need for innovation in the field of cryotherapy. For example, there is a need for innovation with regard to devices, systems, and methods that reduce the need for replacing or recharging refrigerant supply tanks, that facilitate the use of additional types of refrigerants, and/or that have other advantages relative to conventional devices, systems, and/or methods.